Antifuses have been known for some time and are disclosed for example in U.S. Pat. Nos. 3,191,151; 3,742,592; 5,019,878; and 5,298,784. Antifuses are devices which have a high impedance before programming and a low impedance after programming, and are used widely in integrated circuit structures. An antifuse is the converse of a fuse, which can be employed in a similar manner. Use of an antifuse permits the tuning of various analog circuit parameters, the programming of digital logic, and the selection of certain pieces of redundant circuitry. An exemplary application for antifuses (given by way of example only) is to switch desired resistances into a voltage controlled oscillator (VCO), so that the center frequency and range of the VCO will be within desired specifications.
Antifuses can be formed from transistor or diode structures which normally have a high impedance when reverse biased. The appropriate PN junction of the device can be shorted by applying a large reverse bias, causing part of the junction to melt and causing the metal which contacts the junction to flow into the molten region, thereby creating a low impedance metal filament.
Conventional antifuse structures typically require a relatively high programming voltage and energy, which may cause damage to the remainder of the integrated circuit in which the antifuse is located. It is therefore an object of the invention to provide an improved antifuse structure, and a method of forming an antifuse, which require a lower programming voltage and energy than have typically been the case in the past.